I’d be reluctant to actually put this in a wall in a home. having both low voltage and high voltage in the same box is a big NEC no no.

sure they exist… http://en.wikipedia.org/wiki/Relay#Latching_relay

If you were going to put this in a wall, it would be better done in a junction box, separately from the plug itself, then run 14/3 to the plug. For one, it’s not fully accessible to the room. For two, no one expects to see extra electronics behind an outlet. From the electronics side, it’s a good solution. There are commercial alternatives (X10/etc) but this is definitely cheaper.

By the way, I certainly hope that this “hack” is not “news” for anyone reading this website…
Maybe start a Hack101 website for stuff like this and blinking leds?

“By the way, I certainly hope that this ‘hack’ is not ‘news’ for anyone reading this website.”

Because we certainly wouldn’t want any beginners on here getting in the way of all the constructive commentary. Goddamn beginners reminding us that we once knew as little as they did …

oh,I see we have some NEC experts here.

So tell me when it is acceptable to have high and low voltage mixed together?

first one to get it right gets an arduino shoved up their a##

polossatik,

>Maybe start a Hack101 website for stuff like this and blinking leds?

The LED must at least have an Arduino causing it to blink in order to be featured on Hackaday. Everyone knows this.

@polossatik
Wow, this is a new low for hack a day.
driving a relay with an arduino, you almost make it sound that a regular relay is more exciting than a ssr.
Anyways awesome “hack”
/sarcasm
Digikey has multiple ssr’s that source/sink 16 Amps of AC at 120/240V, you could even use those as dimmers.

I would love to read an article that is about what is “the state of the art” for electronic control of mains power – (Inside a wallbox. As in something that meets regulatory standards and doesn’t look shitty.) I know that wouldn’t be a hack – it would be DIYinAProfessionalWayADay.

Everytime someone says “there is a better way to do this”, they need to man up and post their solution to the web.

next time do it wireless, so it will look more from the 2010′s than from the 60′s

@mosheen,
I will not argue theory with you. I will only state that Experience tells me magnetic isolation in the form of a relay is not sufficient to prevent damage to the primary circuit. This goes to Urich’s point about contactors. The spacing and design is such that the isolation is sufficient for protection as well as high inrush current. I don’t think that Kenneth’s intent is to install these in a wall for daily appliances or mass market them so he has an acceptable design. My comment was around a more serious build.

“…no optical isolation…” You do realize that he has magnetic isolation by using the relay. Optical isolation would be redundant and useless.

Posted at 6:24 pm on Jan 31st, 2010 by Odin
_____________________

@Odin: Not redundant, and not useless. It would provide an additional layer of protection, is easily sourced from old modems, and is no more than a passing thought to integrate into the design.

Here’s my hour and a half build circa 2006:

http://img689.imageshack.us/img689/582/box2w.jpg
http://img686.imageshack.us/img686/9158/box1pm.jpg

@Matt – If you’re brewing at home, the built-in thermostats in most refrigerators suck, particularly if you’re using a chest freezer for conditioning. In that case, you can’t get the freezer ‘warm’ enough for the proper conditioning temp.

Sorry I was talking to @odin not you and we are making the exact same point. I suspect those in our background have seen many toasted control circuits because of relays turning into carbon, copper and silver blobs. Not much isolation when that happens.

This project seems to pay a little more attention to safety concerns than some of the other line-voltage “hacks” I’ve seen here, but I’d like to share a few comments.

I agree that a solid state relay might be a better choice than a mechanical relay. I would mount it in an aluminum outlet box, so that the relay can dissipate heat into the housing. Ground the housing for safety.

Solid state relays switch on zero crossings, so they are much quieter, electrically speaking. This is very important if you intend to do any kind of bang-bang control.

One possible downside to solid state relays is that they will *not* switch properly if they are not loaded sufficiently.

Whether you use a mechanical or solid state relay, one thing is clearly missing from this design– a fuse in the 110 “Hot” lead. A fuse goes a long way to protecting your switch gear, maintaining isolation, and protecting your home from fire.

Good job. I would replace the cardboard and use a proto board so you can solder the parts to the board. They only cost about $3 for one that will do what is needed here.

I would also place it in a metal wall box instead of plastic so if something like a fire were to occur you have better protection as well as the casing being grounded for shock prevention.

People saying, ‘use a solid state relay’ need to realize that people have been using this circuit for decades and it is in use in millions of places for a reason, it works and it is safe. The relay is just as good isolation as a optoisolator and often more reliable than solid state relays because it produces no heat and has a very low parts count. Television sets have used this for over 30 years when turning on and off and I don’t see homes going up in flames because of it.

One nice hack you can do with this circuit is to buy a cheap clock or clock/radio. Use an extension cord and cut one of the wires , leave the other wire intact. Inside the radio attach the circuit used here to the alarm function(speaker or piezo) and run the cut wire of the extension cord through the relay. You now have a device that can turn anything on at preset times and depending on the clocks functions turn it off after 15 minutes or 1 hour. I used it for years to wake up to my tv . This was back in the 80′s way before tv had alarm functions.

I would use a solid state relay. Just do a search on ebay. The last one I bought was $6.99 and that was with shipping. It can handle 25 amps and can be switched with 3-32VDC and provides optical isolation. You can drive it directly from a port on the Arduino. It will take a couple of weeks to arrive.

For all you anti-multi-voltage in the same box yahoos check this out-
http://images.betterswitch.com/bs200-a.jpg
This is a UL listed product.
This handy little cube has a total of six wires sticking out of it.
A 120V Hot
A 120V Neutral
A 120V Switch Leg
3 LOW VOLTAGE switch wires
It’s about 1 Inch Cubed
Slam it into a box, or a fixture connect your low voltage t-stat wire that is rated for 300V in the same enclosure and….
BAM!
You have a great little switch system that turns on a light when you open the door or whatever you want it to do really.
You get… If memory serves me correctly 6 Amps of rated contacts. There is no saftey there is no fuse, you only get breaker protection from burning this bad boy out.
Go take your opto-isolators to your pretty PLCs.
Yes opto-isolators have their purpose. You NEED them in certain situations. Usually High Voltage and/or High Current Situations.
And please, don’t even try to argue that 120V 15A is High Voltage and/or High Current.
If I could not mix voltages in the same box as a resi electrician I could not do my job. Yes there are restrictions but opto-isolators are not a necessary requirement of those restrictions.

Another thing. If it’s rated for 6amps where is your fuse? You do know it needs a fuse right? You gung-ho breaker-protected attitude is illegal, and I pray that’s not how you wire peoples homes.

@ jon (first poster.)

Couldn’t you build it into the box in such a way that an optocoupler is the only passthrough?

In fact, use a discrete led and the fiber-optic jacks from some old busted DVD players to make your own opto-isolated box.

I am sure the NEC wouldn’t have a problem with it being optically coupled.

Hi,

from a security standpoint, opto-isolators certainly are a benefit, but they are only required by law (i.e.: “prior art”, “state of the art” clauses), if the relay used is /not itself/ rated for use in such a “class II isolative” protected application.

There are some industry standards (e.g. EN 60335-1, (IEC 60990: 1999) Deutsche Fassung EN 60990: 1999 or DIN VDE 0106), but basically what you want is an isolation that is as effective as an 8 mm creepway on any surface, or 6 kV voltage.

Another good indicator is: can a single, flattened drop of water cause dangeraus loss of insulation?

Other issues are contact current, electromagnetic interference and switching/breaking capacity.

The EMI is adressed with opto-isolating and snubber circuits, for higher currents you need bigger relays, and for higher switching power and breaking capacity you choose a contactor.

If the contact current is rated smaller than the wall outlet rating and a short-circuit or overload can not completely be ruled out, you need an extra fuse.

Btw, if the relay is /not/ rated for protective isolation, then the opto-isolator /must/ be instead.

In most common applications, a protective isolative rated print relay plus a glass fuse is enough.
This applies to most “Arduino” circuits etc.

This is an example for a safe choice of relay:
http://finder.de/comuni/pdf/S40newEN.pdf

If you forgot about building it into the outlet and just made a box that plugs in over the outlet then you do not have to worry about building codes.

If you do this hack and your house burns down, even if it was not the hack that started it, the insurance company will have a good excuse to back out of covering the loss. I would advise that you NEVER do something like this unless it is 100% in line with your building codes.

THIS IS NOT WORTH THE RISK

I’m trying to sense 110v bath fan turning on and subsequently closing a 24v circuit for a heat recovery ventilator controller. I’m stumped by what I see as NEC limitations. Any ideas? I think a 120v coil relay n/o with spdt output side would work, but mixing 600v insulation romex and thermostsat cable in the same box seems to be a no no. Thanks/Don

Totally cold device! I was wondering if there’s something like this readily available on the market. I want to connect a water sensor to a shop vac to collect winter vehical drippings up off my heated garage floor. Any insight would be awesome!